The invention firstly concerns an apparatus for producing plastic containers by means of stretch blowing having, a feed device for feeding an explosive fluid into a combustion chamber and a firing device for firing the explosive fluid in the combustion chamber. In addition the present invention concerns an apparatus for coating the inside walls of a plastic container with a barrier layer which is impermeable in relation to gases, aroma substances and the like, in which a stretch blowing mould is connected by way of a connecting portion to valve-controlled fluid lines in order to fill the container in the mould with at least one gas.
Plastic containers are frequently produced by stretch blow moulding. In that procedure a preform is generally firstly produced by injection moulding. That preform is usually of a diameter which is smaller than the diameter of the bottle to be produced and a length which is shorter than the length of the bottle to be produced. In addition the preform generally already has an opening which is already in the form of the opening of the bottle to be produced. For example the opening can be provided with a screwthread and a holding ring. The preform is then firstly heated and introduced into a stretch blowing mould, the internal space of which corresponds to the finished container. Now, generally by means of a stretching ram which is axially introduced into the preform, the shape is axially stretched. That operation involves producing in the preform an internal pressure which is mostly in a range of between about 5 and about 15 bars. After the preform has been correspondingly stretched the internal pressure in the preform is markedly increased, that is to say to a range of from about 30 to 50 bars, whereby the preform is ‘blown up’ and pressed against the inside wall of the stretch blowing mould so that it assumes the shape of the container to be produced.
WO 98/06559 discloses an apparatus for producing containers. Here, PET bottles are produced by a procedure in which firstly a preform is heated to a temperature of about 100 to 120° C., which is suitable for the stretch blowing operation. That preform is introduced into a tool mould corresponding to the shape of the container and a stretching pressure of at least 2 bars, usually from 5 to 10 bars, is produced. The preform is axially stretched by means of an axial and generally vertically movable stretching ram. Thereupon a blowing pressure which is in the region of 40 bars is produced in the preform. As a result the wall of the preform is pressed against the inside wall of the mould and the container is shaped in that way.
Usually the stretching pressure is produced by means of compressed air. In contrast however, for producing the blowing pressure, there is usually provided a special compressed air container which by virtue of the high pressure necessary is subject to high safety requirements and for that reason the procedure is very expensive.
WO 98/06559 has therefore already proposed that the stretching pressure should be produced by blowing an explosive gas mixture into the preform, for example a mixture of oxyhydrogen gas and an inert gas, and providing the high blowing pressure by firing of the explosive gas mixture, in which case that explosion blowing pressure causes the wall of the preform or the partially pre-moulded container to be pressed entirely against the inside wall of the stretch blowing mould. The procedure also has the advantage that a short-term rise in temperature is produced by the explosion during the stretch blowing operation, whereby the container to be produced is sterilised.
In terms of technical implementation however it has been found that the containers produced with the known apparatus could not be used industrially. They could not be produced and reproduced in adequate quality in terms of their shape and volume and also in terms of their optical appearance. Thus for example it was not possible to produce PET bottles with clear transparent walls. It was assumed that this in part unattractive appearance occurred due to unwanted temperature influences which arose out of an only inadequately controllable explosion.
Therefore DE 199 38 724 already describes an apparatus for producing plastic containers by means of stretch blow moulding, in which the firing device is disposed in the internal space at the apparatus side so that the explosion can be better controlled. The apparatus described herein, in which the preform firstly has to be fixed at one end of a cylindrical receiving means, the side of which that is remote from the preform can be brought into engagement with a distributor block, can however only be used for linear machines as the structure of the distributor block including the firing device is so complicated and bulky that it can only be used in a stationary condition. In addition it has also been found with this apparatus that a proportion of finally moulded containers, which is not negligible, does not comply with the usual quality requirements. That is attributed inter alia to only insufficient mixing of the fluid components forming the explosive gas.